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Ed's SEUL KT88 supply mod thread..

Squidward

Squidward

Scrappy Mod
Subscriber
This amp is not only built from Keg's SEUL KT88 schematic, he sorted out some things in the power supply and I learned a lot in the process.

Anyway, here is my implementation. It weighs in north of 30#, which isn't terrible, and it has no electrolytic caps in it anywhere. We ran it for long stretches at the 'Fest, and I could best describe it's performance as smooth and involving, and it had guts! It didn't hurt that it was paired with Cableguy's AN-Js and Jim's killer CDP.


 
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That's a beaut, Ed! What kind of caps are those (both the filter caps and the blue boxes...)?

I like your innovative mounting schemes, too!
 
I used the same blue film caps in the power supply of Bill's 222C. They are 630vdc, which is hard to find in big film caps. I source them at Mouser, for about 15 bucks a pop for 10uf.
 
Nice looking amp!

And yeah, those big blue Epcos caps are sweet, we use them at work in 2kW bi-directional power converters. If they ever change the design I'm going to be watching the trash like a hawk.
 
I wanted to add that the caps in the main power supply are Cornell Dubilier UNL6W30K-F 30uF 600V capacitors. I couldn't be happier with them for performance. They're a bit pricy, but at roughly $1 per 1uF capacitance, it's not terrible. Think about how much the tubes and transformers cost!
 
Squidward said:
I wanted to add that the caps in the main power supply are Cornell Dubilier UNL6W30K-F 30uF 600V capacitors. I couldn't be happier with them for performance. They're a bit pricy, but at roughly $1 per 1uF capacitance, it's not terrible. Think about how much the tubes and transformers cost!
Click to expand...

I drained one with my finger Sunday and it sure felt like more than 10uf. Getting shocked is one of those things you never totally get used to.
 
Squidward said:
I wanted to add that the caps in the main power supply are Cornell Dubilier UNL6W30K-F 30uF 600V capacitors. I couldn't be happier with them for performance. They're a bit pricy, but at roughly $1 per 1uF capacitance, it's not terrible. Think about how much the tubes and transformers cost!
Click to expand...

not shy on buying good caps...what about the chokes? you spent 3x the amount on a cap that you did on your first choke? ;)
 
Ed, you mentioned that there are no electrolytic caps in the amp. What is the sound quality difference with all PIO caps. Also, (and this is my ignance talking) how do you deal with caps that need to be polarized?
 
I find it hard to comment on the differences this implementation has because of my cap choices, but I will say that it is smooth and powerful. I am pleased with the outcome, and I believe my experiment to be successful.

I used metalized poly, poly, motor run, and those Russian PIOs. It wasn't all PIO. I really like the industrial film type caps coming out from Epcos, ASC, and Cornell Dubilier. I couldn't be happier with the performance of the CD Electrofilms I have in there. The amp is dead quiet, and each channel has less than 100uF filter capacitance.

Non-polar caps can be used in place of polar caps with no problem. It's the other way around that you have to worry!
 
Dual/2 chokes per channel do help out there in the filtering. :thmbsp:

Also from my experience oil/poly/motor run tend to work as though
there a larger cap verse an electrolytic, in other-words for an same
size electrolytic the oil/poly/motor run do more filtering.
 
Squidward said:
The amp has a diet that's high in Iron. What can I say? ;)
Click to expand...

Popeye-Spinach.jpg


It worked just fine for Popeye
 
There is nothing wrong with that choke Ed. :)

I'm just being Overly critical of the amount of resistance to the finals.

I think in a console amp or something with a power transformer that is less stout than what you are running it is well suited... one could put 300-500uf of capacitance after it and make the DCR a non issue.

in an amp such as yours, with its cutting edge "lack of electrolytic capacitors" and power transformer capable of 500ma+ I believe it to be a bottleneck.

being as you are looking to build the exceptional I would be considering what choke to sub in place of that radiodaze budget job to get a cheap upgrade in the mix.

if you could maybe post a schematic of your supply... I've done some sims based on what I think you are running but really don't know.

what is the current draw on that driver stage? (ed or keg?)
 
Rage

Now Sean, everyone has to draw the line somewhere and do what they think is best.
(also many different design philosophies, plus just using some parts on hand to) ;)

So..
Not using a lot of capacitance I'd want an fair amount of inductance, which is what is
going on in this amp, so to me its pretty decent, I see these designs touting a cutting
edge "low resistance" supply then using driver tubes not suited for the job, wheres the
great complete design there. ;) (but those second chokes here could be smaller) :)

----

If your gunna tout 1 aspect, and leave something else not so trivial out it is diminished.
IMHO.. :D
 
I'm not opposed to trying new things. What choke would you sub in for the Hammond 159S? How about the RD-100?

I also wonder how much of your opinion stems from experimentation vs. parroting someone else's line, considering last week you couldn't tell if an amp was rigged for pentode, triode, or UL opperation by reading the schematic? (Oh my, now who's being overly critical! ;) )
 
Kegger said:
Now Sean, everyone has to draw the line somewhere and do what they think is best.
(also many different design philosophies, plus just using some parts on hand to) ;)

SO..
Not using a lot of capacitance I'd want an fair amount of inductance, which is what is
going on in this amp, so to me its pretty decent, I see these designs touting a cutting
edge "low resistance" supply then using driver tubes not suited for the job, wheres the
great complete design there. ;) (but those second chokes here could be smaller) :)

----

If your gunna tout 1 aspect, and leave something else not so trivial out it is diminished.
IMHO.. :D
Click to expand...

we might want to start a new thread on this.. it was rude of me to criticize the choke selection in this thread.


anyhow... keg,

I feel because of all of the help you have offered me over time that if I think I've found a few cool tricks that it sure would be neat so share them with you .

I don't claim any superiority here... the supplies you build sound pretty good to me.


Do you feel though that the amp I presented had rolled off highs? was the driver tube not doing the job from what you heard?

on the same note, having just 2 henries per channel - did you hear hum? was there detail missing?

I really would like your feedback!


Now as to the latter part - it seems to me, on the power supply part of the amplifier .. you design around 1mv of ac to the finals so that you don't need a large r-dropper... you are using the "r-dropper" in your rc stage mostly for decoupling.

so aside from the 1mv paramter, you use the first cap size to get the voltage you want?
 
Squidward said:
I'm not opposed to trying new things. What choke would you sub in for the Hammond 159S? How about the RD-100?

I also wonder how much of your opinion stems from experimentation vs. parroting someone else's line, considering last week you couldn't tell if an amp was rigged for pentode, triode, or UL opperation by reading the schematic? (Oh my, now who's being overly critical! ;) )
Click to expand...

the first part- I need to see the whole supply and what current you are drawing....


the second - a good question.

I've studied more than one guru's practices. I try and steal ideas from each of them... sort of a ****ed up kloodge of ideas from a multitude of characters.


the schematic in question was kind of goofy.. I do believe the original poster posted a new one in that thread. the confusion on my part was the power supply and specifically where the screens were attached.

I do believe your reply was that the amp was "pentode strapped."

you can't "strap a pentode."

in this case the screen was tied directly to the B+. unregluated pentode mode...
 
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